The present invention relates to an inductive coupler, and more specifically to a separable coupler which is operable by electromagnetic induction to transfer electrical power without metal-to-metal contact and adapted for use in a system for recharging a battery for electrically powered vehicles, and the like.
There has been known an inductive coupler which has a primary coil wound around a primary core and connected to the source of electrical power and a secondary coil wound around a secondary core matable or engageable with the primary counterpart, wherein alternating current applied across the primary winding produces a moving magnetic field which in turn induces a voltage in the secondary winding, as a result of which the electrical power is transferred from the primary winding to the secondary winding. The primary and secondary cores may be configured in various shapes, e.g. a channel shape as disclosed in Publication of unexamined Japanese patent application No. 63-151006 (1988), coaxial cylindrical shape as described in Publication of unexamined Japanese patent application No. 63-240331 (1988), and "E" shape such as the one shown in FIG. 1 hereof. The above "E" shaped and coaxial cylindrical shaped cores may also be referred to as "tripod" type cores because of their three-leg configurations as seen in axial cross sectional views thereof. The channel shaped cores may be called as "bipod" type because of its two-legged geometry.
Each core is usually made up of laminations, or a number of laminated thin plates having magnetic properties and insulated from one another. Solid ferrite cores may be used advantageously to reduce the core loss that is caused by high frequency operation of the inductive coupler. It should be noted, however, that the ferrite is hard but brittle, and hence there is a fear that the cores may be nicked or broken at their mating surfaces by the shock of impact caused when they are jointed together for the transfer of the electrical power. Publication of unexamined Japanese utility model application No. 61-177417 (1986) proposes the use of protective layers of resin, such as nylon or Teflon, coated on the mating surfaces of each core to prevent damage to the surfaces. Such a protective resin covering according to the Publication is effective to prevent the possible breakage of the abutment surfaces of the ferrite cores, but it will form a core-to-core gap that corresponds to twice the resin coating thickness. Since even a slight increase in the core-to-core gap will appreciably affect the power transferring efficiency (=secondary effective power/primary effective power), the use of nonmagnetic resin covering on the cores poses a problem in practical application of the inductive coupler.
In the case of laminated cores in which the mating surfaces are defined by exposed ends of the respective laminae, the surfaces tend to become irregular or uneven so that the primary and secondary cores when closed will form a gap therebetween which is large enough to seriously affect the power transferring efficiency.